Optical fiber unit for air blown installation and manufacturing method thereof

ABSTRACT

An optical fiber unit for air blown installation includes at least one optical fiber having a core layer and a clad layer, a protective layer coated on the surface of the optical fiber; and protrusions made of polymer resin and formed on the outer circumference of the protective layer in a banded shape. The protrusions may be formed either by supplying polymer resin to the outer circumference of the optical fiber with passing the optical fiber through an extrusion dice in which grooves of a predetermined shape are formed on a hollow inner circumference thereof, or by supplying polymer resin to the outer circumference of the optical fiber through nozzles with moving the optical fiber in a longitudinal direction.

TECHNICAL FIELD

The present invention relates to an optical fiber unit, and moreparticularly to structure of an optical fiber unit for air blowninstallation and a method for manufacturing the optical fiber unit.

BACKGROUND ART

An optical fiber is broadly used for long-distance rapid transmissionowing to its low transmission loss and great bandwidth. For installationof the optical fiber conventionally, several optical fibers are bound ortwisted to be a cable, and then this cable is installed. In recent, theoptical fibers are generally installed by blown air.

According to the air blown installation, a tube made of polymer materialhaving a diameter of 5 to 8 mm, called a micro tube or duct, is buriedin an installation spot in advance, and then an optical fiber unithaving 1 to 12 cores are installed therein with the use of blown air.The optical fiber installed by blown air (so called, Air Blown Fiber:ABF) is installed using fluid drag force, so it is important that thesurface of the optical fiber is configured to receive more fluid dragforce.

A technique for processing the outer surface of ABF is disclosed in U.S.Pat. No. 5,042,907 that is schematically shown in FIG. 1. As shown inFIG. 1, glass beads 5 are provided on the outer surface of the opticalfiber 1 so that the optical fiber is better affected by the blown air.In other words, the glass beads are stirred together with a coatingresin, and then uniformly coated on the outer surface of the opticalfiber 1. At this time, the size of the glass bead 5 received in theresin 4 of the outer surface of the optical fiber should be relativelylarger than the thickness of the coating layer, and the glass bead 5should have high Young's modulus in order to generate propulsive forcedue to the blown air. However, such high Young's modulus of the glassbead deteriorates bend characteristic of the optical fiber unit. Inaddition, cracks may happen between the glass bead 5 and the resin 4,and these cracks may be propagated inside the optical fiber. In such areason, an intermediate layer 3 should be interposed between an innerbuffer layer 2 and the resin 4 of the outer surface. However, thisconfiguration requires at least three coating processes, therebycomplicating the manufacturing procedure and increasing costs.

Another conventional technique for processing the surface of the opticalfiber is disclosed in U.S. Pat. No. 5,555,335 shown in FIG. 2. Accordingto this technique, after a resin is coated on an optical fiber 1, glassbeads are attached on the outer surface 6 of the optical fiber by meansof static electricity before the outer surface is cured. However, someglass beads are apt to be detached from the outer surface since theadhesive force of the glass beads is not regular on the outer surface ofthe optical fiber. The glass beads not adhered to but detached from theouter surface may damage the optical fiber unit while the unit isinstalled.

As another conventional technique, a dimple may be formed on the surfaceof the optical fiber with the use of foaming polymer materials. However,the foaming polymer material increases the coefficient of friction, soan installation length of the optical fiber for a unit work is too shortand the hardness of the optical fiber unit is too weak.

On the other hand, it has ever been proposed to install a ribbon-typeoptical fiber by winding a fiber of a particular material. However,since the ribbon-type optical fiber has a direction to the bending, theoptical fiber tends to be bent only to one direction.

DISCLOSURE OF INVENTION

The present invention is designed to solve the problems of the priorart, and therefore an object of the invention is to provide an opticalfiber unit for air blown installation which is capable of receiving morefluid drag force by forming protrusions of various types on the surfaceof the optical fiber unit inserted into a tube for optical fiber unitinstallation, and a manufacturing method of the optical fiber unithaving simplified processes.

In order to accomplish the above object, the present invention providesan optical fiber unit for air blown installation into a tube, whichincludes at least one optical fiber having core layer and clad layer; aprotective layer coated on a surface of the optical fiber; and aprotrusion made of polymer resin and formed on an outer surface of theprotective layer in a banded shape.

The protrusion may be formed continuously or discontinuously, and theprotrusion may have a spiral, waved or sine-waved pattern. In addition,the protrusion may have various sectional shapes such as triangle,semicircle, arc, trapezoid, or unevenness.

According to one aspect of the invention, there is provided a method formanufacturing an optical fiber unit for air blown installation, whichincludes the steps of passing at least one optical fiber having corelayer and clad layer through a hollow extrusion dice in which apredetermined groove is formed on an inner surface thereof; and forminga protrusion having a banded shape on the outer surface of the opticalfiber by supplying polymer resin on an outer surface of the opticalfiber so that.

According to another aspect of the invention, there is also provided amethod for manufacturing an optical fiber unit for air blowninstallation, which includes the step of forming a protrusion having abanded shape on an outer surface of at least one optical fiber havingcore layer and clad layer by supplying polymer resin through a nozzle onthe outer surface of the optical fiber while moving the optical fiberalong a longitudinal direction thereof.

Here, the protrusion is preferably formed in a spiral, waved, orsine-waved pattern by rotating the nozzle around the optical fiber orrotating the optical fiber.

In addition, the protrusion may be formed discontinuously by supplyingthe polymer rein on the outer surface of the optical fiberdiscontinuously.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of preferredembodiments of the present invention will be more fully described in thefollowing detailed description, taken accompanying drawings. In thedrawings:

FIG. 1 is a sectional view showing an optical fiber unit according to anexample of the prior art;

FIG. 2 is a sectional view showing an optical fiber unit according toanother example of the prior art;

FIGS. 3 to 5 are perspective views showing protrusions of variouspatterns according to preferred embodiments of the present invention;

FIGS. 6 to 10 are sectional views showing a single-core optical fiberunit of various structures according to preferred embodiments of thepresent invention;

FIG. 11 is a sectional view showing a multi-core optical fiber unitaccording to a preferred embodiment of the present invention;

FIGS. 12 to 15 are sectional views showing multi-core optical fiberunits according to preferred embodiments of the present invention;

FIG. 16 is a schematic view for illustrating a method of manufacturingan optical fiber unit according to an embodiment of the presentinvention; and

FIG. 17 is a schematic view for illustrating a method of manufacturingan optical fiber unit according to another embodiment of the presentinvention.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail referring to the accompanying drawings. Prior to thedescription, it should be understood that the terms used in thespecification and appended claims should not be construed as limited togeneral and dictionary meanings, but interpreted based on the meaningsand concepts corresponding to technical aspects of the present inventionon the basis of the principle that the inventor is allowed to defineterms appropriately for the best explanation. Therefore, the descriptionproposed herein is just a preferable example for the purpose ofillustrations only, not intended to limit the scope of the invention, soit should be understood that other equivalents and modifications couldbe made thereto without departing from the spirit and scope of theinvention.

FIG. 3 is a perspective view showing an optical fiber unit according toa preferred embodiment of the present invention. Referring to FIG. 3,the optical fiber unit of the present invention includes an opticalfiber 10 having core layer and clad layer, a protective layer 20surrounding the optical fiber 10, and a protrusion 30 formed on theouter surface of the protective layer 20.

The optical fiber 10 includes a core layer for transmission of opticalsignals, and a clad layer surrounding the core layer. The optical fiber10 may also include a protective layer made of silicon or similarprotective materials for protecting the inside of the optical fiber fromexternal impurities and moisture. The present invention may adopt eithera single-mode optical fiber or a multi-mode optical fiber, and theoptical fiber may be configured in a ribbon bundle for easy access. Inaddition, the optical fiber may further include an additional protectivelayer, and a coloring layer for identification of the optical fiber.

The protrusion 30 is formed on the outer surface of the protective layer20 so that the optical fiber unit may receive fluid drag force duringair blown installation. The protrusion 30 is formed on the protectivelayer 20 continuously or discontinuously along a longitudinal directionof the optical fiber.

For example, the protrusion 30 may be spirally extended along thelongitudinal direction on the outer surface of the protective layer 20,as shown in FIG. 3. In other cases, a waved protrusion 31 is formed onthe outer surface of the protective layer 20 as shown in FIG. 4, or aprotrusion of another pattern such as a sine-wave (not shown) may beformed thereon.

In addition, as shown in FIG. 5, a lot of protrusions 32 may beirregularly arranged with a space therebetween on the outer surface ofthe protective layer 20 so that the protrusions 32 are discontinuouslyformed. Furthermore, it is also possible to form a protrusion of acontinuous banded shape and protrusions of discontinuous banded blockstogether.

The protrusion may have various sectional shapes such as rectangle,triangle, semicircle, arc, trapezoid, or unevenness.

The protrusion may be made of the same material as the protective layer20. If the protrusion is made of different material to the protectivelayer 20, it is possible to form a coating layer made of glass, ceramicor polymer resin on the surface of the protective layer 20 and theprotrusion(s) 30, 31, 32 or 60 in order to prevent deterioration ofadhesive force due to the use of different materials in advance.

FIG. 6 shows an example of the optical fiber unit according to anembodiment of the present invention. Referring to FIG. 6, a buffer layer(or, a protective layer) 21 surrounds the optical fiber 10. Preferably,the optical fiber unit of the present invention has a circular section,and two protrusions 30 are formed on the outer surface thereof atopposite positions.

FIG. 7 shows another example of the optical fiber unit according to thepresent invention. Referring to FIG. 7, the optical fiber unit includesan optical fiber 10, and a protective layer for protecting the opticalfiber. The protective layer includes a buffer layer 21, and a sheath 25formed on the outer surface of the buffer layer 21. In addition, theprotrusions 30 made of the same material as the sheath are formed on theouter surface of the sheath 25. The sheath 25 is a coating layer made ofdurable materials such as plastic or nylon, and plays a role ofrelieving external impact to the optical fiber unit. In this reason, thesheath 25 preferably has a Young's modulus of 400 to 1000 MPa under thecondition of 2.5 strain, more preferably 500 to 800 MPa under the samecondition. If the Young's modulus of the sheath is lower than the lowestlimit, it is more difficult to install the optical fiber unit with theuse of blown air, while, if the Young's modulus is too high, cracks mayhappen due to the bending.

FIG. 8 is another example of the optical fiber unit according to thepresent invention. The optical fiber unit of FIG. 8 further includes anintermediate layer 24, compared with that of FIG. 7. The intermediatelayer 24 is formed between the buffer layer 21 and the sheath 25, andplays a role of preventing cracks of the sheath 25, if happen, frombeing propagated into the optical fiber unit. In addition, theprotrusions 30 are formed on the outer surface of the sheath 25 forreceiving fluid drag force.

FIG. 9 shows another example of the optical fiber unit according to thepresent invention. The optical fiber unit shown in FIG. 9 is identicalto that of FIG. 7, except that a coloring layer 11 is provided on theouter surface of the optical fiber 10. The coloring layer 11 facilitatesto identify the kind of optical fibers during installation or repair ofthe optical cable. In this example, the protrusions 30 are alsosymmetrically formed on the sheath 25 for receiving more fluid dragforce.

FIG. 10 shows another example of the optical fiber unit according to thepresent invention. The optical fiber unit of FIG. 10 includes theoptical fiber 10 having the coloring layer 11, the buffer layer 21, theintermediate layer 24, and the sheath 25. In addition, on the outersurface of the sheath 25, protrusions 30 having a triangular section areformed at symmetric positions along the circumference of the opticalfiber unit.

FIG. 11 shows another example of the optical fiber unit according to thepresent invention. The optical fiber unit of FIG. 11 includes twooptical fibers 10, each having the coloring layer 11 therearound. Inaddition, the protrusions 30 symmetrically formed on the sheath 25 havea triangular section. The buffer layer 21 surrounding the optical fibers10 has so great hardness to endure external pressure or bending. Forexample, Young's modulus and hardness of the sheath 25 should be largerthan those of the buffer layer 21, preferably at least three times. Inaddition, the intermediate layer 24 formed between the sheath 25 and thebuffer layer 21 should have Young's modulus and hardness larger than thebuffer layer 21. Seeing Young's modulus and hardness of the wholelayers, the sheath 25 has the greatest Young's modulus and hardness, theintermediate layer 24 has Young's modulus and hardness identical to orlower than the sheath 25, and the buffer layer 21 has the smallestYoung's modulus and hardness.

As other examples of the present invention, optical fiber units having aribbon-type optical fiber 40 therein are shown in FIGS. 12 to 15. Theribbon-type optical fiber 40 has a plurality of optical fibers in theribbon, and the plurality of optical fibers are bound with the use of ajacket made of polyethylene (PE), polyurethane or polyvinylchloride(PVC) in a bundle. In addition, when many optical fibers are inserted inthe optical fiber unit as mentioned above, it is also possible toreplace at least one optical fiber with Kevlar (manufactured by DupontCo.).

Specifically, the optical fiber unit of FIG. 12 includes a multi-coreribbon-type optical fiber 40, and a protective layer 50 formed tosurround the optical fiber 40, and protrusions 60 having a semicircularsection are formed on the outer surface of the protective layer 50.

The optical fiber unit of FIG. 13 further includes a sheath 55 and twomulti-core ribbon-type optical fibers 40 are piled up, compared withthat of FIG. 12. The optical fiber unit of FIG. 14 is different fromthat of FIG. 13 only in the point that a coloring layer 41 is formed tosurround each optical fiber in the multi-core ribbon-type optical fiber40. In addition, the optical fiber unit 15 is different from that ofFIG. 14 in the points that an intermediate layer 54 is interposedbetween the protective layer 50 and the sheath 55, and protrusions 60symmetrically formed on the sheath 55 have a triangular section.

Now, a method for forming the protrusion of a banded shape is describedin detail.

The protrusion may be formed using an extrusion process. FIG. 16 is asection view (a) schematically showing an extrusion dice (a mold) usedin a preferred embodiment of the present invention, and a side view (b)showing the extrusion dice seen from an output portion. The extrusiondice 70 coats a protective layer 110 by supplying polymer resin in adirection of the arrow B on the outer surface of an optical fiber 100with passing the optical fiber 100 through a nipple 71 in a direction ofthe arrow A. The output portion is generally formed circular. In thisembodiment, the output portion of the extrusion dice 70 is basicallycircular, and grooves 72 in a shape of triangle, semicircle, arc,trapezoid, or unevenness are formed in the output portion as shown inFIG. 16(b).

Thus, if the optical fiber 100 is passed through the extrusion dice 70and polymer resin is supplied on the outer surface of the optical fiber100 as shown in FIG. 16, the protective layer 110 is coated on the outersurface of the optical fiber 100 and the extrusions of a banded shapeare formed thereon according to the shape of the grooves 72.

On the other hand, the optical fiber 100 passing through the extrusiondice 70 may be a simple-core optical fiber shown in FIG. 11, or aribbon-type optical fiber as shown in FIGS. 12 to 15. Furthermore, theprotrusions of a banded shape may be separately formed while an opticalfiber which is already coated with a protective layer is passed throughthe extrusion dice of FIG. 16. In this case, the protective layer (or, asheath positioned in the outermost layer if the protective layer iscomposed of several layers) may be made of different material to theprotrusion. Thus, in this case, it is preferable to coat glass, ceramicor polymer resin on the surface of the optical fiber having theprotective layer and the protrusions after the protrusions are formed.

Moreover, if the extrusion dice 70 is rotated clockwise orcounterclockwise on a plane perpendicular to the extruding direction orthe optical fiber 100 is rotated, it is possible to make the opticalfiber unit having protrusions of various patterns such as spiral patternor waved pattern. For example, the protrusion 31 shown in FIG. 4 may beobtained by rotating the extrusion dice or the optical fiber inclockwise and counterclockwise directions by turn. In addition, thediscontinuous protrusions 32 shown in FIG. 5 may be obtained bydiscontinuously supplying the polymer resin for formation of theprotrusions. In other words, the protrusions 32 may be formed bystopping supply of polymer resin for a predetermined time or absorbingthe polymer resin to a direction opposite to the supply direction (or, adirection of the arrow B in FIG. 16).

If the protrusions are formed in a spiral or waved pattern and/ordiscontinuously, the optical fiber unit may receive more fluid dragforce during the air blown installation.

FIG. 17 is a schematic view for illustrating a method for formingprotrusions according to another embodiment of the present invention. Inthis embodiment, a nozzle 80 is used for forming the protrusions insteadof the extrusion dice. In other words, at least one nozzle 80 isarranged near the outer surface of the optical fiber 100 which passes toa longitudinal direction (or, a direction of the arrow A), and polymerresin is supplied through the nozzle 80 in a direction of the arrow B sothat the protrusion of a banded shape is formed on the outer surface ofthe optical fiber.

When the nozzle 80 is used, it is possible to make spiral or wavedprotrusions continuously or discontinuously. In other words, if thenozzle 80 is rotated clockwise or counterclockwise on a planeperpendicular to the advancing direction of the optical fiber, or theoptical fiber 100 is rotated, the optical fiber unit having theabove-mentioned protrusions having various patterns such as a spiralpattern or a waved pattern may be obtained. In addition, the protrusionmay be formed discontinuously by stopping supply of the polymer resinfor a predetermined time or absorbing the polymer resin to a directionopposite to the supplying direction of the polymer resin (or, adirection of the arrow B in FIG. 17).

Now, a process of installing the optical fiber unit configured as aboveby means of blown air is described in brief.

Firstly, a tube is installed at a spot where installation of an opticalfiber unit is scheduled, and then an optical fiber unit is blown by airpressure to a desired position by means of an installing machine.Generally, the optical fiber may be installed up to about 1 km at oncewithout connection. If the optical fiber unit is installed in a regionhaving a longer distance than the common cases, the optical fiber unitsare installed from the center of the region to both ends. Or else, airis blown from one end, an optical fiber bundle coming out through theother end is bound, and then the optical fiber unit is installed to aremained area of the region. The optical fiber unit may be installed byblown air by such ways even in a region longer than 1 km. If theinstallation of the optical fiber unit is complete, the optical fiberbundle is exposed as much as the area occupied by the installingmachine, so a separate protective combination tube (or, a closedown) isused to seal the exposed optical fiber bundle.

The present invention has been described in detail. However, it shouldbe understood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the invention will become apparent to those skilledin the art from this detailed description.

INDUSTRIAL APPLICABILITY

According to the optical fiber unit for air blown installation and itsmanufacturing method, a continuous or discontinuous protrusion of abanded shape is formed on the surface of the optical fiber unit so thatthe optical fiber unit may receive more fluid drag force during theinstallation process. In addition, the optical fiber unit basically hasa circular section, so it is possible to reduce the direction of opticalfiber unit during the installation process.

Moreover, since the optical fiber unit of the present invention does nothave expensive beads which are conventionally used, there is no need toconduct a process of mixing or stirring beads to resin used for formingan outer coating and a process of forming an intermediate layer. Thus,productivity is increased and manufacture costs are lowered.

In addition, since the protrusion is made of the same material as theouter coating layer or coated by the same material as the outer coatinglayer though the protrusion is made of material different from the outercoating layer in the present invention, adhesive force between thecoating layer and the protrusion is not deteriorated.

1. An optical fiber unit for air blown installation into a tube,comprising: at least one optical fiber having core layer and clad layer;a protective layer coated on a surface of the optical fiber; and aprotrusion made of polymer resin and formed on an outer surface of theprotective layer in a banded shape.
 2. An optical fiber unit for airblown installation according to claim 1, wherein the protrusion isformed discontinuously.
 3. An optical fiber unit for air blowninstallation according to claim 1, further comprising a coating layercoated on the surfaces of the protrusion and the protective layer andmade of one selected from the group consisting of glass, ceramic andpolymer.
 4. An optical fiber unit for air blown installation accordingto claim 1, wherein the protrusion has a spiral, waved or sine-wavedpattern.
 5. An optical fiber unit for air blown installation accordingto claim 1, wherein the protrusion has a sectional shape of triangle,semicircle, arc, trapezoid, or unevenness.
 6. An optical fiber unit forair blown installation according to claim 1, herein the protective layerincludes a buffer layer surrounding at least one optical fiber, and asheath surrounding the buffer layer.
 7. An optical fiber unit for airblown installation according to claim 6, wherein the buffer layer hasYoung's modulus and hardness smaller than the sheath.
 8. An opticalfiber unit for air blown installation according to claim 6, wherein anintermediate layer is provided between the buffer layer and the sheathin order to damp external impact.
 9. An optical fiber unit for air blowninstallation according to claim 8, wherein Young's modulus and hardnessof the intermediate layer are smaller than those of the sheath andlarger than those of the buffer layer.
 10. An optical fiber unit for airblown installation according to claim 1, wherein the protrusion is madeof the same material as the protective layer.
 11. An optical fiber unitfor air blown installation according to claim 1, wherein the opticalfiber includes a multi-core ribbon-type optical fiber, and theprotective layer has a circular sectional shape.
 12. A method formanufacturing an optical fiber preform for air blown installation,comprising: passing at least one optical fiber having core layer andclad layer through a hollow extrusion dice in which a predeterminedgroove is formed on an inner surface thereof; and forming a protrusionhaving a banded shape on the outer surface of the optical fiber bysupplying polymer resin on an outer surface of the optical fiber sothat.
 13. A method for manufacturing an optical fiber unit for air blowninstallation according to claim 12, in the protrusion forming step,wherein a protective layer is formed on the outer surface of at leastone optical fiber, and the protrusion is formed on an outer surface ofthe protective layer.
 14. A method for manufacturing an optical fiberunit for air blown installation according to claim 12, in the protrusionforming step, wherein the protrusion is formed in a spiral, waved, orsine-waved pattern by rotating the extrusion dice around the opticalfiber or rotating the optical fiber which is passing through theextrusion dice.
 15. A method for manufacturing an optical fiber unit forair blown installation according to claim 12, further comprising thestep of coating any of glass, ceramic and polymer resin on the surfaceof the optical fiber having the protrusion.
 16. A method formanufacturing an optical fiber unit for air blown installation accordingto claim 12, in the protrusion forming step, wherein the protrusion isformed discontinuously by supplying the polymer rein on the outersurface of the optical fiber discontinuously.
 17. A method formanufacturing an optical fiber unit for air blown installation,comprising: forming a protrusion having a banded shape on an outersurface of at least one optical fiber having core layer and clad layerby supplying polymer resin through a nozzle on the outer surface of theoptical fiber while moving the optical fiber along a longitudinaldirection thereof.
 18. A method for manufacturing an optical fiberpreform for air blown installation according to claim 17, in theprotrusion forming step, wherein the protrusion is formed in a spiral,waved, or sine-waved pattern by rotating the nozzle around the opticalfiber or rotating the optical fiber.
 19. A method for manufacturing anoptical fiber unit for air blown installation according to claim 17,further comprising the step of coating any of glass, ceramic and polymerresin on the surface of the optical fiber having the protrusion.
 20. Amethod for manufacturing an optical fiber unit for air blowninstallation according to claim 17, in the protrusion forming step,wherein the protrusion is formed discontinuously by supplying thepolymer rein on the outer surface of the optical fiber discontinuously.